Steel Production Based on the Blast Furnace Route

1 Steel Production Based on the Blast Furnace Route 

The main route from iron ore to steel is via blast furnaces to produce molten iron (pig iron) from iron ore, coke and air. The coke is produced in coking plants from hard coal. Once the iron is refined in the blast furnace, the hot metal is transferred to the basic oxygen furnace, where pure oxygen is blown into the liquid pig iron through a water-cooled lance. The carbon content is reduced by oxidation to CO 

In former times, two other processes were also used to burn out the excess carbon and other impurities for the production of steel from pig iron. In the Bessemer process, air was blown through the molten iron. The bottom of the converter was perforated with a number of channels through which the air is forced into the converter. The process was rapid (about 15 min) and so there was only little time for chemical analysis and adjustment of the alloying elements in the steel. Bessemer converters also did not remove phosphorus efficiently, and certain grades of steel were sensitive to nitrogen, which is the major part of the air blast. 

The second forerunner (and competitor for some time) of the basic oxygen furnace was the open hearth furnace [Siemens-Martin (SM) process], where the oxidative effect was achieved by addition of scrap, iron ore, lime, and some air, which release oxygen into the iron melt. 

Bessemer processes and most open hearth furnaces were closed by the early 1970s and 1990s, respectively, not least because of their fuel inefficiency and problems with dust removal (SM process). Nowadays, they are almost completely replaced by oxygen furnaces. 

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